In commercial packaging applications such as commercial cigarette packaging, it is desirable to produce a packet which is decorative and which is durably sealed. Such packets are generally prepared from preformed cardboard blanks, which have been decorated or contain printed areas on one side of the blank. The blanks may be precreased, and are designed to be folded and bonded in a manner so as to create a complete packet.
Packets, for example, cigarette packets, may be produced in a continuously operating packing. Cardboard blanks are fed from a stack to a folding station. A measured number of cigarettes is foil-wrapped, for example with an aluminum foil, and then fed onto a cardboard blank to be folded and sealed, or bonded. An adhesive is applied to the areas of the blank to be bonded, generally to the side and top flaps. The areas to be bonded are then compressed and a completed packet is released from the packing machine.
Bonding of the cardboard blank to form the packet generally is accomplished by the application of an adhesive to specific areas of the blank, for example, on the side and top flaps or corner flaps of the lid. Bonding is completed by compressing these areas with the complementary area of the blank to be bonded. The adhesive is generally a hot-melt adhesive or a cold glue. In order to permit better adhesion of the areas to be bonded, conventional printed cardboard blanks have no printing in the areas to be bonded.
Many commercial packaging applications require the use of cardboard blanks which have been laminated on one surface, generally the decorative surface, with plastic films. Because the plastic films and the cardboard web are generally laminated as a uniform surface material, the areas to be bonded are not excluded from the lamination.
Problems arise when using plastic coated blanks, however. Packets produced from plastic coated blanks may not be stably bonded, because the hot melt adhesives conventionally used for example, in the bonding of cigarette packets, do not adhere adequately to plastic-coated surfaces. For example, at increased temperatures as in summer, a separation of the bonded areas of a cigarette packet takes place, particularly the side or top corner flaps of the packets.
In addition, the bonding of packets which have bevelled or chamfered longitudinal edges, for example, those disclosed in European Patent No. EU-A-1 0204 933, is particularly problematic, because the cross-sectionally octagonal or side area-rounded packets provide a smaller adhesive surface for bonding, and because such hinge-lid packets are exposed to higher loads of lateral pressure, for example, in the user's pocket.
Other adhesives, such as fast-action or secondary adhesives are not suitable to overcome these bonding problems, as their contact with the contents of, for example, a cigarette packet may lead to an increased risk to the health and safety of the consumer
It would be of great utility to provide an adhesion process for durably bonding cardboard blanks which have been laminated with a plastic film using conventional hot melt adhesives.